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A given CPU normally notes a new grace period during one RCU_SOFTIRQ, but avoids reporting the corresponding quiescent state until some later RCU_SOFTIRQ. This leisurly approach improves efficiency by increasing the number of update requests served by each grace period, but is not what is needed for kernels built with CONFIG_RCU_STRICT_GRACE_PERIOD=y. This commit therefore adds a new rcu_strict_gp_check_qs() function which, in CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, simply enters and immediately exist an RCU read-side critical section. If the CPU is in a quiescent state, the rcu_read_unlock() will attempt to report an immediate quiescent state. This rcu_strict_gp_check_qs() function is invoked from note_gp_changes(), so that a CPU just noticing a new grace period might immediately report a quiescent state for that grace period. Reported-by Jann Horn <jannh@google.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.